This invention relates to the provision of standards that can be readily and reliably used in analyses, one important application being the anaylsis of air pollutants. With increasing population, pollution problems increase, it seems, exponentially rather than linearly. Thus, vastly improved methods for analyzing impurities in the atmosphere are urgently needed.
There are, of course, many efficient analytic methods and apparatus such as gas chromatography, infra-red, among other techniques. In present methods for preparing gas standards for use in air pollution analyses one employs precision flow systems, permeation tubes, gas mixtures contained in metal cylinders or spray cans and the pyrolysis of organic materials at high temperatures using a carrier gas stream. However, disadvantages exist in the present approaches. For example, the flow dilution method requires the use of extensive gas flow trains in order to reduce gas concentration to a low level. Permeation tubes require individual calibration, and the rate of gas diffusion through the tube is very sensitive to temperature changes. While the spray can or cylinder standards are convenient, the gas or gases therein can react with or adsorb on cylinder walls over extended time periods. The pyrolysis technique is accurate under controlled conditions, but presently this approach is limited to sulfur dioxide, and analysis is difficult because certain detectors do not give reliable results if sulfur compounds other than sulfur dioxide are present, for example, inadvertently due to imcomplete pyrolysis.
Thus, an object of this invention is to provide methods and materials for primary standardization which avoid certain existing problems in the analytic field. Another purpose is the provision of readily portable standards which can be prepared easily just before use and which afford a wide variety of test conditions. A still further aim is the provision of materials and methods for readily custom-building a standard for use in a given situation, including immediate, on-location testing. These and other objectives will appear hereinafter.